Limit switch



W. C. M UTH LIMIT SWITCH July 25, 1950 2 Sheets-Sheet 1 Filed July 12, 1946 T T 0 E N E Y y 1950 w. c. MUTH 2,516,525

LIMIT SWITCH Filed y 12, 1946 2 Sheets-Sheet 2 IN VEN TOR. W/LHELM C, MUTH A T OENEY Patented July 2 5, 1 950 UNITED STATES PATENT OFFICE LIMIT SWITCH of Ohio Application July 12, 1946, Serial N 0. 683,054

4 Claims.

This invention pertains to an improved limit switch and particularly to a thermostatically controlled electrical switch and circuit closer mechanism, and more particularly to a duplex apparatus for automatically opening and closing different circuits alternately.

While the present invention is applicable to a wide range of uses, fOr illustrative purposes, but without intent to unduly limit the application or scope of the invention, it is herein shown and described as an automatic heating furnace control for either hold fire or high limit operation for which it is especially desirable, but ob- Viously is not limited thereto. The present instrument may be so mounted as to be responsive to temperature fluctuations of a furnace jacket bonnet or of a flue pipe or stack and serve to energize damper actuating means for fuel feeding mechanism as necessitated by current heating requirements.

The present invention is a further development and amplification of that disclosed in Letters Patent of the United States to Carlson, No. 2,213,621 of September 3, 1940.

The object of the instant invention is to simplify and improve the construction, as well as the means and mode of operation of thermostatically controlled electrical switching and circuit opening and closing mechanisms, whereby they may not only be economically manufac tured, but will be more eil'i'cient in use, capable of application to a wide variety of purposes, automatic in operation, uniform in action, having minimum number of working parts, and be unlikely to get out of repair.

A further object of the invention is to provide adjustable timing means for varying the period of response of the instrument to temperature change.

A further object is to provide such a limit switch comprising a rotatable actuating member such as a cam and a mounting member carrying one or more contacts and a contact blade and a support bracket for said blade, said base and the parts carried thereby being rotarily adjustable about the axis of rotation of said actuating member to vary the temperature at which the actuating member actuates the blade, said blade support means being also adjustable relative to the support base to permit adjustment of the blade relative to the contact or contacts.

Another object is to provide improved magnetic means to provide snap action make and break of the several circuits.

A further object of the invention is to provide a duplex automatic circuit controller, possessing the advantageous structural features, the inherent meritorious characteristics and the improved mode of operation herein set forth, or their equivalents.

With the above primary and other incidental objects in view as will more fully appear in the specification, the invention intended to be protected by Letters Patent consists of the features of construction, the parts and combinations thereof, and the mode of operation, or their equivalents, as hereinafter described or illustrated in the accompanying drawings.

In the accompanying drawings, wherein is shown the preferred, but obviously not necessarily the only form of embodiment of the invention,

Fig. 1 is a perspective view of an assembled thermostatically energized electrical limit switch, embodying the present invention.

Fig. 2 is a front view thereof.

Fig. 3 is a longitudinal sectional view thereof.

Fig. 4 is a diagrammatic view of a system of electrical circuits under control of the instant instrument.

Fig. 5 is a fragmentary View showing the contact spring in its original untensioned position.

Fig. 6 is a view similar to Fig. 5, but showing the spring in its normal tensioned position.

Like parts are indicated by similar characters of reference throughout the several views.

In the drawings, 1 indicates a helically Wound bimetal thermally responsive element through which extends a rock shaft 2, to the extremity of which one end of the bimetal element 1 is attached at 3.

The opposite end of the thermally responsive spring 1 is attached to a relatively fixed sleeve 4 through which the shaft 2 axially extends. This thermally responsive portion of the apparatus is enclosed in a tubular heat conductive housing 5 closed at its extreme end and having at its opposite end a bushing 6 and lock collar '1 surrounding the sleeve 4 and engageable with a mounting plate 8, which may be attached to a portion of a furnace jacket bonnet wall or a :portion of a flue or stack pipe.

Mounted on the forward end of the sleeve 4 is a housing 9 enclosing the contact members, their mounts and the actuating head, and having therein a bearing 2a for the shaft 2, mounted on a bridge 90. within the housing 9. Carried on the flanged face of the housing 9 are two contact mounting segments. One such mounting segment II is normally fixed, but is adjustable with- 3 in the range of segmental slots !2 through which engage clamp screws i l. ihe other mounting segment I5 is pivotally mounted concentrically with the housing 9 preferably on the stem or rock shaft 2 for manual oscillatory adjustment thereabout. On each of the mounting segments 5 I and E5 a bracket i6 is mounted for oscillatory adjustmentabout a pivot ll within therange of an arcuate slot it through which a clamp screw 19 extends. Each of the brackets l6 carries a flexible spring contact arm or blade. The spring arm or blade 2:! of the stationary mounting segment H is alternately engageable. witheach of.a pair. of relatively spaced contacts 2! and 22. The cor responding adjustable mounting segment lfi carries a spring contact arm 23 alternately engageable with spaced contacts 2d audit. The spring arms 29 and 23 are normally biased toward each other by adjustment of the brackets it, whereby they tend to engage the innermost contacts 2! and i i-of. the respectivepairs thereof, under the inherent. tension of the spring arms Etand 23.

Fixedly attached. tothe end ofthe rock shaft or.

stemi, for. unison motionintermediate. the spring arms 25) and 2-3 is an oscillatoryactuating mem.- ber orcam 26.- lhe cainzhis rotated to and fro as. thebimetal thermally responsive element is actuated in accordance. with fluctuations oftemperature. The cam may engageone or the other of the spring arms, thereby overcoming the inherent. bias. of. the engaged spring arm andbreaking its contact with the inner. or normally engaged contact Her 24 causingit to engage the other contact of the particular pair thereof.

In.order to give. to the spring arms actuated by theoscillatorycam a snap actionanddefinition to their movement, a permanent magnet 2'! is mounted on the corresponding mounting sector adjacent to the contact toward which the spring arm is fiexe'dlbythe cam, which accelerates its movement and insuresfum. contact engagement'.

A detachable cover can 28 engageablewith the housing 9., encloses spring arms, contacts and oscillatory sector. An arm 29 upon the. adjustable mounting segment iil'extends beyond theperiphery, of the housing 3 and cover. cap. 28, to enable: the. segment Hiand with it the spring arm .23 and; coactingcontacts .Zt'and 2.5:, to be shifted circumferentially, thereby advancing or delaying the engagement of the cam. Ztwith the arrnZt and movement of thelatter away from contact 2d into engagementw-rrith contact 25. When under increased temperature, the stress of the bimetal element increases, and the shaft or stem 2' is rocked to move cam 26 out of its engagement with the spring armiiil the latter disenga es the;contact 22 and. by its, inherent tensionnreturns. to engagement with the opposite contactzl. continuedrotation the. cam 21% engages theopposite spring arm 23 to break its contact withthe contact 2d and flex the arm into engagementwith the companion contact 25. The interval between The arrangement. is: such that a lower temperature is requiredto cause the cam 2'5 to engage the springarm 23 when themounting segment 15'. is. atonelimitpfitslrange of adjustment. (mild) thaniwhen it. is.

oscillated to the opposite limit of its range of movement (cold).

A connection panel 3| surmounts the housing 9 having thereon a series of circuit terminals, the conductors from which extend through the Wall of the housing 9 to the various contacts.

Because of excessive range" of temperature tending to actuate the cam Ztto an extreme position no positive stop is provided, but after having initially actuated the engaged spring arm, the cam. 26 is capable of further idle operation in which the cam periphery merely wipes upon the spring. arr-asunder. continuing influence of the thermostatic spring I without further moving the engaged spring and therefore without straining or breakageof parts, and without causing the springs, either: contact or thermostatic, to take a definite set.

Iii-operation, the switching unit functions as a hold-fire or high-limit control, depending upon the. condition of thefireasrisreflectedby the bonnetor. stack temperature. If. the fire is within normal limits, the. camlfi does not contact eitherspring armlfl: or 23. These arms therefore remain intheir normal or biased positions, in engagement with the contacts 21 and 24, respectively. In this position, the switching unit. performs merely a coupling function, serving. as a terminal board through which thefurnacecontrol. 32 isoperatively connected with the room thermostat 33. Solong as the switching unit remainsinits normalposition, operation of. the furnace control.unittlzisunderzthe sole control of. the. room thermostat, andresponds to a call for. heat by the room. thermostat. increasing,com-

bustion in the furnace, or. by reducing combustion insthefurnace when theroom thermostat is satisfied...

Power. for the furnace control 32is supplied :by the secondary of a transformer 34. through. the wires 352 and-.36. The.v room thermostat andthe limit switch comprising; the subject matter of they presentinvention areconnected. to the furnace control by meansof. the terminals-37, 38 and 3.2:; Terminal 38 is. the. OE or stop terminal while the terminal.39 controls.the.on or. start. operation of the .contro1.32. The twocircuits. are completed. through; the. common. terminal 3'3.

Asshown inlligl 4, the system. is inits. off or stopposition. Should. the room thermostat 33.

callforheat, the armwillmove .from the.off or; stop.contact...4t1to.the on or startcontact: 4|. This movement of:the roomthermostat moves the furnace control unit32 to its..onf. oristart position, it being energizedzby the; following circuit; from the common-terminal?! conductor. t2 leads to terminal 43.011 the panel 3] of the switching unit. Fromthere, through theinternal wiring of the limit switch, the current is carried through conductor. Metoithespring. arm 23 and thence through contact 24 and.conductor. 4'5. to .theterminal ltlon the panel. .3] Eromxterminal 4620011- ductorll. leadstotheroom thermostattB. The circuit. is. completedfromthe thermostat through contact. ll, conductor. 48. to. theterminall lll on the. panel 3I,.and.thence.through conductor: 51L to. terminal 39 ofithefurnace control 32.

The furnace: controlremains in. its on. or. start. position. until. the room. thermostat. 33 is:

satisfied, at which. time, thethermostatmoves from contact :to-contact .40 thereby movingthe furnacacontrolto:its01f orzstopposition The circuit: ion the. offi movement. of the furnace control is the same.aslafor:ithe:on movement 3 from the commonlterminal 31 of:the furnace control tothe thermostat 33. From the thermostat however, the circuit is completed through contact 40, and conductor to terminal 52 on the panel 3|.- From terminal 52, the internal wiring of the switching unit carries the current through conductor 53 to the spring arm 20, thence through contact 2 I, conductor 54, conductor 55 to terminal 56 on the panel 3|. Conductor 51 interconnects terminal 56 with the off or stop terminal 38 on the furnace control thereby completing the circuit to move the furnace control to its off position.

Should an abnormal fire condition arise at any time, such condition is rectified by automatic operation of the limit switch of the present invention. For example, if during the on period of operation of the furnace control, as called for by the room thermostat 33 the flue or bonnet temperature should become dangerously high, the present switching unit responds to such abnormal condition by energizing the off or stop circuit of the furnace control. An increase in flue or bonnet temperature causes clockwise rotation of the cam 26 thereby moving the spring arm 23 away from contact 24 and into engagement with contact 25. Such movement of the arm 23 opens the circuit to the room thermostat thereby eliminating the overall control by the room thermostat, and substitutes a circuit to the off or stop terminal 38 of the furnace control. The new circuit is the same as before described from the common terminal 31 of the furnace control to the spring arm 23. From the arm 23 however, the circuit is completed through contact 25, conductor 55, terminal 56 on the panel 3| and conductor 51 to the off or stop terminal 38 of the furnace control. The furnace is therefore shut off because of the increase in the flue or bonnet temperature above a predetermined safe maximum.

- Another abnormal condition which is cared for and controlled by the present switching unit, is a decrease in flue or bonnet temperature when the room thermostat does not call for heat during extended periods. These periods usually occur in the early fall and late spring, when because of the ambient temperature, the thermostat remains satisfied for long periods of time. During these periods it is quite possible for the fire to become quite low, or extinguished because of the lack of periodic firing operations. The low fire is reflected by a decrease in the stack or bonnet temperature, and when such temperature falls below a predetermined minimum, the cam 26 of the present switching unit by movement in a counter-clockwise direction, moves the spring arm from contact 2| into engagement with contact 22. Such movement of the arm 20 sets up a new circuit to energize the furnace control so as to move it to its on or start position. Such on operation of the furnace control is entirely independent of any demand by the room thermostat 33.

Referring again to Fig. 4 in which the system is shown in its off or stop position with the room thermostat fully satisfied as shown by its engagement with contact 40, upon movement of the arm 20 into engagement with contact 22, the on circuit is completed as follows. From the common terminal 31 of the furnace control the circuit to the thermostat 33 is the same as heretofore explained. The circuit to arm 20 is through contact 40, conductor 5|, terminal 52 on the panel 3| and conductor 53. The arm 20 being in engagement with contact 22, the circuit is completed to the on terminal 39 of the fur nace control through contact 22, conductor 58, terminal 49 on the panel 3|, and conductor 5|]. Thus the furnace control 32 is energized so as to move to the on or start position independently of the room thermostat 33.

Should the room thermostat 33 call for heat during the on operation of the furnace control under control of the arm 28, the thermostat moves from contact 40 to contact 4|, thereby establishing the normal on circuit which is completely independent of the on circuit controlled by the arm 20. Upon moving of the thermostat from the contact id into engagement with the contact 4|, the special control circuit through the arm 25 is broken thereby relieving the switch 2U22 of all control functions, even though the arm 20 remains engaged with the on contact 22.

The housing 5 surrounding the bimetal spring I, as shown in Fig. 3, is employed only when the switch is used in the furnace, flue or stack. If used as a bonnet switch, the housing 5 is eliminated, as shown in Fig. l.

The contact surface of the cam or actuator 26 is concentric with its axis of rotation whereby it makes only point engagement with one or the other of the straight fiat circuit closing arms. The construction is such that after having initially engaged and moved the circuit closing arm, the actuator may continue to rotate to greater or less degree, without varying the adjustment of the circuit closer arm.

From the above description it will be apparent that there is thus provided a device of the character described possessing the particular features of advantage before enumerated as desirable, but which obviously is susceptible of modification in its form, proportions, detail construction and arrangement of parts without departing from the principle involved or sacrificing any of its advantages.

While in order to comply with the statute the invention has been described in language more or less specific as to structural features, it is to be understood that the invention is not limited to the specific features shown, but that the means and construction herein disclosed comprise the preferred form of several modes of putting the invention into effect, and the invention is therefore claimed in any of its forms or modifications within the legitimate and valid scope of the appended claims.

Having thus described my invention, I claim:

1. A limit switch for use in a temperature control system adapted. to control the rate of operation of a heat supply device for supplying heat to a space, such as a furnace, which system is of the class which includes a thermostat to be located in said space, and heat supply control means adapted to be electrically controlled by said thermostat to control the rate at which said heat supply device supplies heat to said space, said limit switch device comprising a structure adapted to be connected between thermostat and said heat supply control means and so associated with said heat supply device as to be responsive to a condition existing therein, said switch structure comprising thermo-responsive means adapted to be influenced by the temperature of such a heat supply device, a. rotary actuator operated by said thermo-responsive means, at least one mounting member arranged for rotary adjustment around the axis of rotation oi said actuator, a supporting bracket on. said. mounting. member, a. swingable contact blade carried by said supporting bracket in a position.

where it may be engaged by said actuator, and at least one contact supported on said mountin member in a position where it is engageable by said contact blade, said supporting bracket being adjustable relative to the mounting member, whereby the contact blade and contact together may be adjusted rotarily relative to said actuator for adjusting the temperature at which the actuator engages the contact blade for adjusting its relationship to the contact, and whereby the contact blade may be independently adjusted relative to the contact.

2. A limit switch for use in a temperature control system adapted to control the rate of operation of a heat supply device for supplying heat to a space, such as a furnace, which system is of the class which includes a thermostat to be located in said space, and heat supply control means adapted to be electrically controlled by saidthermostat to control the rate at which said heat supply device supplies heat to said space, said limit switch device comprising a structure adapted to be connected between said thermostat and said heat supply control means and so associated with said heat supply device as to be responsive to a condition existing therein, said switch structure comprising thermo-responsive means adapted to be influenced by the temperature of such a heat supply device, a rotary actuator operated by said thermo-responsive means, two mounting members arranged for rotary adjustment around the axis of rotation of said actuator, a supporting bracket on each of said mounting members, a swingable contact blade carried by each of said supporting brackets in a position where it may be engaged by said actuator, and at least one contact supported on each said mounting member in a position where it is engageable by said respective contact blade, said supporting brackets being adjustable relative to the mounting members, whereby the contact blades and their respective contacts may be adjusted, together rostarily relative to said actuatorf'or adjusting; the temperature at which. the-actuator engages one cr another contact blade foradjusting its relationship to the contact, and whereby the contact blades, may be independently adjusted relative to their respective contacts.

3. Aiimi-t switch for use ina temperature control system adapted to control the rate of operation of a heat, supply device for supplying heat to. av space, such as a furnace, which system is of the class which includes a thermostat to be located-in said space, and heat supply control means adapted to. be electrically controlled by said thermostatto control the rate at which said heat supply device, supplies heat to said space, said.

limit. switch device comprising a structure adapted to be connected between said thermostat and said heat supply control means and. so associated with said, heat supply device as to be responsive to a condition existing therein, said switch structure comprising thermo-responsi've means adapted to be influenced by the temperature of such a heat device, a rotaryactuator operated by saidz-thermo-responsive means, at: ieastc'ne.

mounting .member arranged .forxrotary adjustmentaroundotheaxisof rotation ofsaid actuator, a supporting bracket on. said mounting member, aswingablecontact bladev carriediby said sup-- porting bracket in a position. .where it may be engaged .by. said actuator, and two contacts supportedonv said mounting member in a position where they. are alternately engageable by said contactblade, said. supporting bracket being adjustable relative .to the mounting member, whereby the contact blade and contacts together may be adjustedrotarily relativeto saidactuator for adjusting .thetemperature at which the. actuator engages .thecontact bladefor adjusting Ill 181G134? tio-nship to the contacts, and, whereby the contact blade may be independently adjusted relative to thecontacts- 4.. A limit switch for use in a temperature control. system adapted to control the rate of operation. of a heatsupp'ly device for supplying heat tda. space, such as a furnace, which system is of the class which includes a thermostat to be located in said space, and heat supply control means adapted'to be electrically controlled by said thermostat to control the rate at which said heat supply device suppliesheat to said space, said. limit switch device comprising a structure adapted to be connected between said. thermostat andsaidheat supply control mean and so associated with said heat supply device as to be responsive. toa condition existing. therein, said switch; structure, comprising thermo-responsive means adapted to be influenced by the temperature of such a heat supply device, a rotary actuator operated: by said. thermo-responsive means, two mountingmembers. arranged for rotary ad.- justment around the axis of rotation of said actuator, a supporting: bracket on each of said.

mounting members, a swingable contact blade carried by eachof said supporting brackets in a position where it may be. engaged by said actuator, and twocontacts supported on each said mounting. member in a. position Where they are alternately engageable by their respective contact blade, said supporting brackets being adjustable relative; to their mounting members, whereby the contact; blades andxtheir respective contacts. may be adjusted; together rotarily relative to said. actuator for adjusting thev temperature at which theactuator engagesone or; another contact blade for adjusting its: relationship to their respectivev contacts, andwhereby the contact blades may be independentlyadjusted. relative to their respecfive-contacts,

WILHELM. C. MUTH.

REFERENCES CIT-Ell The: following references. are: of record in the file ot this: patentr' UNITED STATES'PATENTS Number Name Date 70,994 Draper Mar. I5, 1892 674,029 Stolz May 14, 1901 1,458,924 Banan June 19, 1923 1,976,954 Manta Oct. 16, 1934 2,213,621 Carlson Sept. 3, 1940' 2,344,767 Dillman Mar; 21, 1944 

